Process of isomerizing dialkyl benzenes



invention herein described.

Patented July 9, 1946 s PATENT OFFICE PROCESS OF ISOMERIZING DIALKYLBENZENES.

Edward D. Reeves, Cranford, N. J., assignor to Standard Oil DevelopmentCompany, a corporation of Delaware N Drawing.

The present invention relates to the isomerization of aromatichydrocarbons and pertains more particularly to the catalyticisomerization of ortho substituted dialkyl benzenes."

It has been known that ortho xylene and other corresponding orthosubstituted dialkyl benzenes could be isomerized to meta and para formsusing aluminum chloride as the catalyst and, if desired, hydrogenchloride as the promoter. It has also been known in the past toisomerize and disproportionate such ortho dialkyl benzenes undertemperatures of the order of 1300 F. to 1420 F. in the absence of anycatalyst. These methods are, however, disadvantageous for severalreasons. In the first instance, where aluminum chloride is. employed,the catalyst is generally not recoverable and considerable amounts offeed stock were lost due to reaction with the catalyst to form complexeswith aluminum chloride. Furthermore, by the complex formation over anextended period of time, large losses of aluminum chloride" occurred forthe same reason. This, of course, necessitates replacement of thecatalyst mass with aluminum chloride or the complete shutdown of a unitwhile fresh catalyst mass is substituted for the spent mass. In the caseof the thermal isomerization of ortho xylene or other ortho substituteddialkyl benzene, the fuel requirements and the demand for special alloysteel capable of withstanding high temperatures and pressuresnecessitate the expenditure of large sums of money, and from theeconomic standpoint such 'a'process is not particularly desirable wherecommercial scale operations are contemplated.

It is an object of the present invention to carry out the isomerizationand disproportionation of ortho dialkyl benzenes to produce thecorresponding meta and para isomers in the presence of novel catalystcompositions. It is a further object of the invention to obtainsubstantial amounts of meta and para dialkyl benzenes by theisomerization and disproportionation of the corresponding ortho dialkylbenzenes through the use of novel catalyst masses which are relativelystable during the isomerization and'are recoverable for regeneration andreuse in the process. It is a further object oi theinvention to conservefeed stock and to prevent disintegration and degradation of the feedstocks and catalysts employed in the isomerization and.disproportionation of ortho dialkyl benzenes to form the correspondingmeta and para' forms thereof. Other objects will be apparent upon afuller understanding of the Ap'pueation August 18, 1943, Serial No.499,117

10 Claims. (Cl. 260-668) The present invention resides in thepreparation of novel catalyst compositions which, upon being used in theheretofore-mentioned isomerization reaction, obviate the difficultiesheretofore encountered in the known processes; Where a liquid or vaporphase feed stock predominating in or composed solely of ortho dialkylbenzenes is fed at a temperature between about 500 F. and about 1150 F.,at a throughput of between about 0.4 and 6.0 liquid volumes of feed pervolume of catalyst mass per hour, in contact with a novel catalystcomposition which may comprise a synthetic alumina-silica catalyst mass,sufiicient superatmospheric pressures are employed within the lowerportion of this range, that is, at at'emperature below 650 F. tomaintain liquid phase operation if desired. Superatmospheric pressuresmay also be employed where vapor phase reaction is contemplated,generally the pressure amounting to from'1.5 to 10 atmospheres. Thenovel catalyst mass may be prepared in a number of various ways. Thus,for example, a silica gel may first be formed by acidifying a dilutesolution of sodium silicate with a moderate excess of an acid such ashydrochloric acid whereby a desired silica hydrogel is obtained. Thismay then be filtered and washed to remove the sodium ions therefrom,after which the gel may be washed with ammonia to free it of acid ionsand thereafter-heated to a relatively low temperature to evaporate thewater. During the final stages of heating, however, the temperature isgradually raised to a temperature of 800 F.

and maintained at that temperature for a period of 3 hours to effect thefinal drying of the silica gel. This procedure is described in thePatrick Patent No. 1,297,794. To this silica gel produced in accordancewith this method or any other suitable method there is added aluminaeither as a gelatinous precipitate of aluminum hydroxide, as aluminahydrogel, alumina hydrosol or alumina el, or Activated Alumina, andthemixture is commingled with heatingto produce the final dried productwhich serves as the catalyst in the present reaction. A homogenizationtreatment of the silica and alumina may be employed if the hydrogel ofalumina and the hydrogel of silica are first mixed together thenhomogenized and finally dried to remove the water contained therein. Asuitable catalyst composition for use 7 in the present reaction containsabout 87.5 weight percent of silica gel. and about 12.5 weight per centof alumina. The mass may contain a total general a smaller percentageThe catalyst may also be prepared in accordance with the procedureoutlined in U. S. application No. 233,159, filed October 4, 1938, inwhich a mixture of silica and alumina is formed by combining the aluminawith silica while the latter is in hydrous form and thereafterdehydrating the hydrous silica.

A still further method for the preparation of catalyst compositionsuseful in carrying out the process of the present invention resides inthe impregnation of silica gel with a dry powdered alumina while thesilica gel is in the form of hydrogel and thereafter converting the saidhydrogel into a dry gel. A still further method of preparing the novelcatalyst composition resides in impregnating a silica gel with analuminum compound capable of being decomposed either by heat or bychemical reactioninto the oxide such as,

for example, aluminum nitrate, aluminum chloride or aluminum acetate,followed by the suitable treatment to reduce the compound to thealuminum oxide in situ. A solution of aluminum sulfate may be added to asilica gel either in the form of the hydrosol or as the dried gel. Theresulting mixture may then be soaked with ammonium hydroxide toprecipitate the aluminum hydroxide. The mixture then is washed free ofacid and base ions and calcined at a temperature of around 800 F. togive the required catalyst. Upon using aluminum nitrate, acetate orchloride, the oxide is derived therefrom merely by heating the masswithout resorting to the use of ammonium hydroxide to. convert it to thealuminum oxide first. Plural gels of alumina and silica, wherein bothare formed simultaneously in admixture with each other, are contemplatedas well.

Other methods of preparing the catalyst are likewise known. However, theinvention is not limited to any specific method for preparing the mixedsilica-alumina catalyst mass. In general, the mass may contain from 2:1to as high as :1 mols of silica per mol of alumina, although molarratios outside of this range may likewise be employed withoutappreciably affecting the efficiency of the catalyst for isomerizing theortho dialkyl benzenes, as more fully hereinafter described.

In addition to the use of catalysts composed exclusively of silica andalumina as above described, the invention also contemplates the use ofcatalysts containing, in addition to the silica and alumina, smallamounts of metal oxides such as magnesia, thoria, zirconia and the oxideof boron. These catalysts may be prepared by the addition of thecorresponding nitrates, acetates or hydroxides of these metals to thehydrogels followed by the addition of ammonium hydroxide to obtain amixed mass of hydrated alumina and/or hydrated silica coupled withhydrated thoria, hydrated zirconia, hydrated boron oxide or hydratedmagnesia. The resultant admixture is filtered and dried and after dryingto a temperature of from 300 F. to 400 F. at first, and finally at atemperature of 800 F. to 900 F., the resultant catalyst mass is readyfor use. The percentage of the various metal oxides other than thesilica and alumina present in the catalyst mass may range between about3% and 10% based on the silica-alumina present, although percentagesoutside of these ranges may be employed if desired.

As previously stated, the resultant catalyst mass is employed incarrying out the isomerization of the ortho dialkyl benzenes by-acombined isomer- 4 ization and disproportionation reaction to producethe corresponding meta and para dialkyl benzenes. Feed stocks which aresuitable for use in the reaction comprise any one or more of thefollowing substances: ortho Xylene; 2-ethyl toluene; 1,2-diethylbenzene; Z-n-propyl toluene; 2- isopropyl toluene, and similar Ca, Caand C10 aromatic ortho dialkyl benzene fractions. These may be obtainedfor use in the present process through the recovery of ortho Xyleneconcentrates or C9 aromatic fractions obtained in the catalytichydroforming of petroleum fractions, or the feed stock may also beobtained from selected fractions of the required boiling ranges obtainedin coal tar distillations. The ortho Xylene concentrate may be easilyisolated from the hydroformed product by efficient fractionaldistillation as may the C9 aromatic fraction which usually containssubstantial amounts of ortho dialkyl benzenes. Also suitable feed stocksare obtainable by taking the selected cuts and fractions of aromatictype from products obtained in the catalytic cracking of petroleumrefinery fractions. The process finds its greatest utility ,at thepresent time in using '18 heretofore-mentioned feed stocks. It isrecognized, however, that the isomerization reaction involves theattainment of an equilibrium and that the process is also applicable tothe isomerization of meta and/or para dialkyl benzenes to produce thecorresponding ortho isomers thereof. Thus, too,,a meta substituted typeof feed stock yields ortho and para isomers; a para type yields orthoand meta isomers.

In general, the temperature lies between about 500 F. and about 1150 F.,although it is preferred to operate between about 750 F. and about 1025F. In general, the throughput rate is between about 0.4 and about 6.0liquid volumes of feed stock per volume of catalyst per hour, butpreferably the rate of throughput lies between about 0.6 and about 4liquid volumes offeed stock per volume of catalyst per hour. The processof the present invention is readilyadaptable to commercial operationsinvolving a continuous vapor phase operation in which the vaporized feedstock is passed through a bed of catalyst mass maintained under therequired reaction conditions. This catalyst mass may be maintained onstream for between about 1 hour and about 20 hours, preferably betweenabout 2 and about 12 hours, after which it is removed from the reactionand the catalyst mass is subjected to a short regeneration treatmentinvolving 1 to 5 hours, preferably between about 2 and about 3 hours,wherein air or any other gas containing free or uncombined oxygen indilute form is passed therethrough for a sufficient length of time andunder controlled temperature such that the carbonaceous impurities areburned from the pores of the catalyst mass within the time required,after which the regenerated catalyst may be again placed on stream foreffecting and activating the isomerization reaction. One of the chiefadvantages of the present process resides in the fact that the need forregeneration of the catalyst mass at frequent intervals is umiecessarybecause even at the relatively high operating temperatures the cokeformed on the catalyst mass is of the order of 0.6 weight per cent whilemaintaining an ortho xylene conversion, of 60% or better. The process isreadily adaptable for combination with other petroleum refiningoperations regardless of whether or not the present operation is carriedout using'a catalyst involving a fixed bed, a moving bed or a fluidcatalyst type of technique.

tofore described.

The process may be worked in conjunction with those processes previouslymentioned which provide the source of orthoxylene or other ortho dialkylaromatics, such as hydroformingor catalytic cracking, and the Xprocessisparticularly The syntheticalmnina-silica catalyst may be employed notonly in the form of granules of highly -porous structure but it may befirst pilled with graphite or starch and'regenerated to render it evenmore highly porous, or. the catalyst may be pilled with. graphiteorstarch and used ,fresh ,in the [an-stream operation without firstregenerating the same, although it is preferred to regenerate thecatalyst if in the pilling operation eithergraphite or starch has beenadded as a cohesion agent.

A series of experimental runs were made to de- The purest product. sofar as the production of meta and para xylenes are concerned,was-obtained when the per cent of ortho xylene undergoing reaction(conversion) was about his gave a selectivity of about 98. Byselectivity is meant the percentage of ortho xylene converted .to metaand para xylenes and ethyl benzene.

However, the utilityv of the invention includes the formation. of lowerboiling aromatics such as toluene or ethylbenzene, the concentration ofwhich is. much greater when higher conversion leveIsare employed,The'pl'oducts need not be termine the reaction variables employed from Iwhich a number of observations can be made. At a given throughput the.temperaturemaintained in the reaction zone has a pronounced effect onthe conversion. For example, by increasing the temperature from 750 F.to 975F. while maintaining 0.6 liquid volume of feed. per volume ofcatalyst per hour the conversion was increased from 44% of the orthoxylene to 77% thereof.

illustrated inj the following table:

Weight 'per cent conversion at the indicated 7: l rate I 0.5 1.8 a 1140It is observed that at a given temperature the conversion decreases withincreasing feed rate. Thus, at 1000 F. the conversion drops from 79% to52.5%, while the liquid volume of feed stock per volume of catalyst perhour is increased from 0.6 to 4.0. In general, if reaction occurs, thefinal product in connection with the isomerization anddisproportionation of ortho xylene has the following weight per centcomposition:

Weight per cent Ortho xylene 34 Meta xylene 49 Para xylene l2 Ethylbenzene 5 The feed stock employed in this particular series of runs hadthe following composition:

7 Weight per cent Ethyl benzene 0 Para xylene 0-1 Meta xylene 6.5-7Ortho xylene 84-87.5 91-95 Total aromatics g silicaand 12.5 weightpercent alumina.

segregated into their'respective constituents since practically all ofthem have excellent blending values for usein aviation fuels or insafety fuels.

: Weight per eent Weight per cent Weight per cent Weight per cent totalliquid gas coke conversion 900 F. 975 F. 900 F. 975F. 900F. 975F.

acemes While :higher gas yields are obtained at the higher temperatures,the total liquid recovery is excellent in the entire temperature rangeshown. The coke formation was so lowthat it was difficult to determinewhether the indicated independence of temperature level was real or was'due' to an experimental error. It was found also that not only did theselectivity decrease with increasing conversion but that this was notaffected by the temperature of the operation, the length of time ofon-stream. operation f the catalystor-th. throughput of.ther feed stockthrough the catalyst mass. The experimental findings were obtainedbypassing the vapor of a C8 aromatic fraction having a boiling range of290-293" F. and of th heretofore-specified composition through a closedreaction tube filled with about 200 cc. of analumina-silica catalystwhose composition was, roughly, 87.5 weight per cent The products werecondensed and collected, theprodnot analyzed for constituents ranginginboiling point between about 265 F. and about 295. F.

H Arun carried out at 985 F. with a throughput or 0.6.liquid volume offeed per volumeof catalyst perhour for 12' hours produced a productcontaining 4 weight percent ethyl benzene, 16 weight per cent paraxylene, 49 weight per cent meta xylene and 26 weight per centunconverted ortho xylene. The yield of the product was about 7 5% basedon the feed stock, with 12%1of the product in the benzene range and 3%accounted for by gas and coke produced.

A considerable number of experimental runs were carried out on two-hourreaction periods using a fixed bed of 200 cc. capacity through which theheretofore specifically mentioned feed stock was passed in the vaporphase. The products obtained varied in composition but generally rangedwithin the following composition:

, Weight Per cent Ortho xylene 26-42 Meta Xylene 31-49 I Para xylene3-17 Ethyl benzene 0-5 Total aromatics produced 93-97 The particularpercentage of constituents in the final product as heretofore mentionedvaries conconditions employed, but in general the product obtained willvary within the heretofore-mentioned ranges. The product may be isolatedthrough fractional distillation means or it may be employed in the formproduced directly as a blending agent in aviation or safety fuels.Appreciable amounts of benzene and toluene were obtained wheretemperatures in the upper range or the heretofore-mentioned temperatureranges were employed with relatively low rates of throughput. Thus, forexample, when employing 0.6 volume of feed stock per volume of catalystper hour while maintaining a temperature of 1025 F. the result was theproduction of from to 23% of toluene out based on the ortho 'xylene fedto the reaction zone. The same run produced, on the same basis, from3.5% to 6% of a benzene fraction. 'In a commercial operation, however,the use of a temperature of this order would call for the use of athroughput of from 3 to 3%; liquid volumes of feed stock per volume ofcatalyst per hour if it were desired to obtain as high a yield aspossible of the meta and para xylenes.

Having thus described and illustrated the nature of the invention, whatis desired to be secured by Letters Patent is:

1. .A'prooess for the isomerization of ortho dialkyl benzenes whichcomprises contacting a feed stock comprising essentially said orthosubstituted dialkyl benzenes at a temperature between about 500 F. andabout 1100 F. with a catalyst mass comprising a synthetic alumina-silicagel for -'a sufficient length of time to form substantial amounts ofmeta and para isomers, said gel con-- taining at least one oxide takenfrom the group consisting of boron oxide, thoria, zirconia and magnesia.

2. In a process of catalytically isomerizing 1,2 dialkyl benzenes toform the corresponding 1,3 and 1,4 dialkyl benzenes under isomerizationreaction conditions, the improvement comprising catalyzing the saidreaction with a, catalyst mass comprising a synthetic alumina-silicagel, containing at least one oxide taken from the group consisting ofboron oxide, thoria, zirconia and magnesia.

3. A process which comprises isomerizing ortho xylene at a temperaturebetween about 500 F. and about 1'100 F. at a throughput of between about0.4 and about 6.0 liquid volumes of ortho xylene per volume of catalystmass per hour while in contact with a synthetic alumina-silica mixedgel, containing at least one oxide taken from'the group consisting ofboron oxide, thoria, zirconia and magnesia.

4. A process which comprises isomerizing a feed stock comprisingessentially ortho xylene at a temperature of about 985 F. at athroughput of about 0.6 liquid volume of feed per volume of catalyst perhour while in contact with a catalyst of silica gel containing aluminaand at least one oxide taken from the group consisting of boron oxide,thoria, zirconia and magnesia.

5. A process as in claim 4 wherein the feed stock is a Ca aromaticfraction obtained from a catalytic cracking of a petroleum oil.

6. A process as in claim 4'wherein the feed stock is a Ca aromaticfraction obtained from the hydroforming of a petroleum fraction.

'7. A process for the production of meta and para xylene which comprisescontacting a feed stock comprising essentially ortho xylene at atemperature between about 750 F. and about 1025 F. a-ta throughput ofbetween about 0.6 and about 4.0 liquid volumes of feed stock per volumeof catalyst per hour with a catalyst comprising essentially syntheticalumina-silica gel, containing at least one oxide taken from the groupconsisting of boron oxide, thoria, zirconia and ma nesia.

8. A process as in claim '7 wherein the catalyst mass is employed in thereaction for a period of time between about 6 and about 12 hours andregenerated with a gas containing free or uncombined oxygen for betweenabout 2 and about 3 hours prior to being re-employed for activating theisomerization reaction, and so employing said regenerated catalyst.

9. A process for the production of 'meta and para-dialkyl benzenes whichcomprises contacting a feed stock comprising essentially thecorresponding ortho dialkyl benzenes at a temperature between about 750F. and about 1025* F. at a throughput of between about 0.6 and about 4.0liquid volumes of feed stock per volume of catalyst mass per hour withcatalyst comprising essentially synthetic alumina-silica gel, containingat least one oxide taken from the group consisting of boron oxide,thoria, zirconia and magnesia.

10. A process as in claim 9 wherein the catalyst mass is employed in thereaction for a, period of time between about 6 and about 12 hours andregenerated with a gas containing free or uncombined oxygen for betweenabout 2 and about 3 hours prior to being re-employed for activating theisomerization reaction, and so employing said regenerated catalyst.

EDWARD D. REEVES.

